This invention relates to a method of producing board material using an autoclave for aging treatment, and more particularly to a method which enables drying of the aged boards in the same autoclave.
In the manufacture of boards and inorganic material, such as those containing calcium silicate, the board is finished by painting plastic substance onto the board after aging. Usually, an autoclave is used for the aging treatment. The water content in such treated material is excessively high so that the board must first be dried before painting.
When an autoclave is used for aging, the water content of the board depends upon the period of aging, temperature of the steam used, etc. Ordinarily, the water content falls to about 50% after formation of the board, in the aging process. The board must then be dried to a water content of 14 to 20% before any painting operation.
Heretofore, hot air driers have been used for drying the hardened material. But disadvantageously, the equipment and process required for such hot air drying are too expensive to enable such method to be used on an industrial basis. Also, it has been found that such hot air drying causes warping of the material, and in the case of board material produced by the paper making process, such hot air drying causes exfoliation between the layers. Thus, the board material after drying was not optimally suitable and also was expensive.